I have a dumb question: Is there enough frozen water on Mars that if it were liquid would be enough to fill the Valles Marineris?
If not, then all we could hope for is to have the water (which always seeks the lowest level, to accumulate there?
Mars has a lot of water locked up in its ice caps and underground. Perhaps enough to be self-sufficient. The asteroids between Mars and Jupiter could be used to make even more water.